Turbulent pneumatic driers for granular and pulverulent material



Sept. 15, '1959 B. SKOGLUND 3 3 TURBULENT PNEUMATIC DRIERS FOR GRANULAR AND PULVERULENT MATERIAL Filed Sept. 25. 1957 Flljl..

INVENTORZV BENGT SKOGLUND TURBULENT PNEUMATIC DRIERS FOR GRANU- LAR AND PULVERULENT MATERIAL Bengt Sloglund, Stockholm, Sweden, assignor to AB Svenska Flaktfabriken, Stockholm, Sweden The present invention relates to apparatus for regulating the treatment time of the material in turbulent pneumatic driers for granular or pulverulent material, so that a product of uniform dryness is obtained, even if the material consists of particles having sizes and shapes varying within a very great range. The present application is a continuation-in-part of my co-pending application, Serial No. 595,461, filed July 2, 1956, now abandoned.

Granular and pulverulent materials of different kinds can suitably be dried pneumatically, i.e., by being fed into a gaseous medium flowing through a tube, which medium has been given such a condition that it can function both as a transporting and drying medium. In order to obtain the necessary drying time within a limited space such drying apparatus is preferably made as turbulent pneumatic driers, i.e., made with a vertical conically widening tube, wherein an upwards directed medium current thus will have a continuously decreasing velocty. The quan tity of medium is adjusted in such a manner that the flow velocty in the widest section of the tube will be below the velocty at which the wet particles remain in suspension. When the material particles reach this level, they will accordingly drop backwards in the tube to a level, where the medium velocty is greater and thus, the particles are entrained again by the medium current. In this way, the material will remain in suspension within a limited section of the widest part of the tube, which part thus forms the drying zone proper. As the particles are dried and become lighter, they will be carried by the medium current out from the drying apparatus and a natural adjustment of the treatment time is thus automatically obtained. When drying materials consisting of particles having size and shape varying within a very great range, however, it has proved difiicult, if not impossible, to select a proper medium velocty, as the velocty for keeping smaller wet particles in suspension often is below that for keeping larger dry particles in suspension. The result will be a material output of highly varying moisture ratio.

The invention provides a drier which eliminates the above mentioned drawbacks, and is characterized in that the fiow velocty in the widest section of the tube normally is held at a value somewhat below the velocty which is necessary for keeping the smaller material particles in suspension, said flow velocty momentarily and with certain intervals being increased to such a high value that the drying medium can carry and transport away from the drying plant also the large material particles being dried to the desired moisture ratio. The velocty is increased when the material held in suspension in the medium current increases" the pressure in the lower part of the tube above a predetermined value, and efiects a discharge of the large particles from the drier. When the discharge is suficient to reduce the pressure in the lower part of the tube, the velocty is decreased to afiord retention of the material in the tube. By adjusting the lower medium velocty in such a manner that a sufiicient drying time is obtained for small and medium-sized material tetas Patent ice particles, the greater part of the material contained in the drying zone will be transported out from the drying apparatus and only particles being more difficult to dry will remain for a continued treatment. At the same time as the velocty of the medium is increased, the feeding of wet material should be interrupted in order to prevent undried material from being caried away by the medium current.

In practicing the invention, the variations of the flow velocty of the medium can Conveniently be carried out by means of a damper in the inlet pipe` for the medium which is preferably supplied by a fan. The damper is operated by a motor governed by a device respon'sive to the pressure in the drying tube, and throttles the medium quantity during the periods of low pressure so that a desired low velocty is obtained and at periods of high pressure, the` damper entirely opens the supply pipe, so

that the maximum medium quantity is free to pass the drying apparatus. Another way to vary the flow velocty of the medium is to regulate the medium quantity by means of guiding vanes arranged at the suction side of the fan or to use a two-speed motor for the fan. The increase of the flow velocty can also be performed by switching on an additional fan for the medium. The invention is not limited by the methods or the means for the adjustments of the dillerent medium velocities, which methods and means can be Varied within the scope of the invention.

The invention will now be described more in detail with reference to the accompanying drawing illsutrating a suitable apparatus for the performance of the method, in which Fig. 1 is a view partially in section of one embodiment of the invention; and

Fig. 2 is a fragmentary plan View showing another em bodiment of the invention.

In the drawing 1 designates a vertical turbulent pneumatic drier, in the lower part lb of which the material to be dried is fed through a chute 2, a sluicing device 3 and a pipe 4. The material meets an upwardly moving current of drying medium, which is supplied through a pipe 5 to the drying apparatus from a fan 6. The fan, which is driven by a motor 7, is in the shown case connected to the suction side by means of a pipe 8 with an attached heating element 9 for the heating of the drying medium. By means of a damper 10 arranged in the pipe 5 the medium quantity is throttled, so that the flow velocty of the medium in the widest part la, the drying zone, of the drying apparatus is maintained at a low value below the velocty, at which the material just remains Suspended. By means of a device 11 responsive to the pressure in the drying tube, and manenvering motor 12, the damper 10 can momentarily fully open the passage-way of the supply pipe, so that the medium quantity will increase to obtain in the drying zone a flow velocty which exceeds the velocty at which the larger dried material particles just remain Suspended. At such an increase of the flow velocty, the greater part of the material in the drying zone is transported `out from the drying apparatus at the point 11 and is separated from the medium current in a cyclone or a similar device (not shown in the drawings).

Fig. 2 illustrates the aforementioned embodiment of the invention wherein an additional fan for the drying medium is switched on. In this embodiment of the invention, two fans 6a and 6b are connected to the supply pipe Sa. The fan 6b is switched on intermittently, for example by a pressure-responsive device 1151 and the fan 6a is continuously driven. Both fans are fed from a common supply pipe 8a having a medium conditioner at 9a.

Thus, in the operation of the drier, the wet material is fed into the drying tube and is Suspended in the up- `and the device 11 operates to reduce the velocity of the medium and renstate operation of the feeding device 3.

I claim:

In a turbulent pneumatic drier for granular and pulverulent material, comprsing a substantially vertical tube, having a continuously upwardly increasing cross-sectional area, circulating means to direct a current of drying medium into and upwards through said tube, alternatively at high and low velocties, and means to introduce said material into said current at the bottom of said tube to dry the same, the medium at said low velocity maintaining the small partcles of said wet material in suspension at the large cross-sectional area of said tube, the medium at said high velocity entrainng the dried partcles of said material and carrying them through and past the large cross-sectional area of said tube, the improvement which comprises a pressure-responsve device in said tube at the lower part thereof connected to said circulating means operable upon an increase in pressure above a predetermined value to efiect said high velocity flow of the medium through said tube, and upon a decrease in pressure below `said predeternined value to efiect said low velocity flow of the medium through said tube.

References Cited in the file of this patent UNITED STATES PATENTS 2,550,374 Palmer Apr. 24, 1951 2,636,642 Gorin Apr. 28, 1953 FOREIGN PATENTS 285,038 Great Britain May 9, 1929 647,657 Great Britain Dec; 20, 1950 

